1. Field of the Invention
The present invention generally relates to a plasma etching method. More particularly, the present invention relates to a plasma etching method for performing etching by means of plasma generated by high-frequency electric discharge to form concave parts and/or opening parts on a surface of a substrate in a manufacturing process for a silicon microprocessing type device.
2. Related Arts
In a manufacturing process for a silicon microprocessing type device such as a pressure sensor and an acceleration sensor, concave parts, which forms a thin part serving as pressure detecting parts, and/or opening parts are formed by means of etching method performed from the rear surface of a semiconductor substrate after the formation of an element part on the main surface of the semiconductor substrate. As a means for forming the concave parts and/or opening parts, a method of anode coupling type plasma etching by using a reactive gas plasma has drawn attention as disclosed in the Japanese Unexamined Patent Publication No. 2-275626, for example.
In the above processing technique, etching speed should be high, the side walls of the concave parts should be perpendicularly etched and the roughness of the etching surface should be small. Particularly, as the concave parts should be deeply formed to some degree, etching amount should be increased, and therefore it takes a longer time to complete etching and further increase in the etching speed has been desired.
As methods for increasing the etching speed, it is conceivable that the applying electric power should be increased, the reactive gas pressure or gas flow rate is increased or the substrate is heated. However, any of these methods directly or indirectly results in the increase in ion energy shot to the substrate, which increases the electric potential of the surface of the substrate.
When a semiconductor element part has been formed on a surface of the substrate (on the opposite side to the etching surface) beforehand, like a pressure sensor, generally an insulating film is formed on the surface of the element part, and furthermore, a resist material, etc, are coated thereto prior to the etching to protect the circuit formed thereon. If the substrate arranged as above is etched, the insulating film or the resist material comes to contact the grounding electrode, whereby the electric charge accumulated on the surface of the substrate can not move, and therefore the electric potential of the substrate turns to be in the floating state. As a result, damage may be caused such as partial breakdown to the insulating film, comparatively large leak current caused by the occurrence of fixed electric charge due to the fixation of excessive electric charge to lattice defect, and the lowering of the amplification factor of the transistor.